Natural curly hair or frizzy hair frequently causes many hair styling problems. For example, the hair tends to spread uncontrollably, hair tips curl up and/or it is difficult to be arranged tidily. A number of methods have been proposed for curing these problems of curly or frizzy hair. A typical cure is the so-called permanent straightening treatment, a chemical treatment which comprises fully cleaving disulfide bonds in hair keratin through a chemical reduction process and stretching the hair by adhering it to a panel or combing it. The straightened hair is then oxidized and fixed to restore the disulfide bonds in the hair, thereby permanently straightening the hair.
Hair which has been artificially permanently waved can be sufficiently straightened by this method. However, natural curly hair or frizzy hair can hardly be straightened by this method, or even when it has once straightened by this method, it returns to its original curly state within several days. To solve this problem, JP-A-60-21704 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a method which comprises heating the reduced hair with an iron in addition to the conventional permanent straightening treatment, to enhance the efficiency of deformation of the hair through thermal denaturation and further reduction. JP-A-59-90508 proposes another method which comprises reducing the hair, steaming the reduced hair and then reducing the resulting hair again with the first pack of reducing agent in the form of a gel. A severe treatment aiming at achieving improved straightening effects would seriously damage the hair. Thus, attempts have been made to improve straightening effect with less damage by using sulfites of a weak reducing capability, or substances similar thereto, by lowering the pH value of the first reducing pack, or by using a specific activator or an oily material in combination.
DE 3535351 discloses a hair straightening composition in which a solvent (such as N-methyl-pyrrolidone) and a reducing agent are used in combination. Further, U.S. Pat. No. 4,963,349 and EP 363057 disclose an aqueous permanent waving lotion containing a 1,3-alkaneldiol including a 2-alkyl-1,3-alkanediol and a 1,3-alkanediol.
However, none of the aforesaid methods and compositions can sufficiently straighten natural curly hair or frizzy hair.
Thus, there is an urgent need to establish a hair straightening composition and a method whereby natural curly hair or frizzy hair can be sufficiently straightened without significant damage to the hair.